Dynamoelectric device



De@ 8, 1942 l E. o. scHwElTzEFz,A v.JR 2,304,604`

DYNAMO-ELECTRIC P'EVICE lPatented Dec.` 8, .1942

UNLTED STATES j PATENT y oFFIc nrNAMoELEcrmc DEVICE Edmund 0. Schweitzer, Jr., Northbrook, Ill. Application November 25, 1940, Serial No. 366.959

s claims. (c1. 172-278) A further object of my invention is to providel I y for superimposing a uni-directional flux component onthe alternating flux component in the stator of an alternating current motor for operating its rotor at a predetermined synchronous speed.

It is another object of my invention to subject the rotor of an alternating current motor to alternating ilux .along one axis and to uni-directional flux along another axis angularly related to the ilrst axis. y

Other objects of my invention will, in part, be obvious and in part appear hereinafter.

For a more complete understanding of the nature and scope of my invention, reference can be had to the following detailed description, taken together with the accompanying drawings in which:

Figure 1 diagrammatically illustrates a conventional form of self-starting induction motor having circuit connections to an alternating current source in accordance with this invention so as to operate the rotor at a synchronous speed;

Figure 2 is a view, similar to that shown in Figure l, illustrating another form of rotor construction; I' n Figure 2A is a perspective figures, the magnetic core being omitted for the sake of clarity; I

Figure 3 is a view, simila'to that shown in Figure 2, with a modified circuit arrangement for `generating the uni-directional ileld;

'still anshading windings or rings 2I and 22 are provided character I designates, generally, 'a synchronous motor system arranged and constructed l-in accordance with the present invention. The motor I0 includes a stator II having a generally C- shapedv configuration and formed of laminations of suitable magnetic material such as silicon steel.

The stator I I is provided with an energizing winding I2 that is connected by' conductors I3 and Il through a variable resistor I5 for energization across a source I6 of alternating current, such as a 60-cycle 11G-volt source. Y

The opposing ends of the C-shaped stator II form pole'members I1 and I8 having arcuate faces between which a rotor I9 is rotatably mounted. The rotor I9 is preferably formed by a stack of laminations of silicon steel and is provided with bars or conductors 20' extending through. the stack and f' interconnected at their ends to provide a squirrel cage rotor construction.

` In order to provide a self-'starting construction,

in the pole members I1 and I8 respectively so as to shift a portion of the 'alternating flux in time and space with respect to the remaining portion of it. 'I'he construction of the motor III thus far described is conventional and has been widely used for operating devices requiring relatively small;

' amounts of power, such as electric fans and the members I'I and I8, the full synchronous speed view of the rotor bars and end discs shown in Figure 2 and the following of the rotor I9 is 3600 revolutions per minute or revolutions per second when the source I6 is a 60-cycle source. However, the squirrel cage rotor I9 will rotate at a speed which is somewhat less than the full synchronous speed in developing suilicient power to cause its own rotation and the rotation of the load to which it may be connected.

When the revolutions per second of the squirrel cage rotor I8 equal a. certain fractionalv part lof the frequency of the alternating current source Il, then the -flux produced by the current flow through the conductors 20 is stationary: that is,

the positions of the poles of the magnetic ileld created by the rotor currents do not change because. these currents alternate at the same rate as the rotor I 9 turns. It the rotor I 9 is then subjected to .a uni-directional flux, a definite synchronous torque is produced. For example, if the two pole induction motor III is energized from a 60g-cycle source I 6 and the rotor I9 runs ata speed oi thirty revolutions per second or with a 5,0% slip. the frequency of the rotor current will 15 be thirty cycles per second. i The two pole stator l ployed in lieu of the rectifier 23.

. or 1200 revolutions per minute.

II induces two poles in the rotor I3 so that with the rotor I9 running at a speed of thirty revolutions per second and carrying thirty cycle current as a result of the 50% slip it will generate a two pole field of fixed polarity in xed direction in space. This will be clear when it is recalled that the rotor is turning at the same speed as the rotor current alternates. Now if a uni-directional eld is applied to the rotor I9, a synchronous torque results which prevents any change in the position of the axis of the rotor field in relation to the applied uni-directional field. The only power requiredof the supply generating the uni-directional field is that necessary to provide sufcient excitation, as in the case of a synchronous alternator. Also, as in the case of the synchronous alternator, the amount of direct current excitation generating thefuni-directional field controls the power factor of the alternating current supplied to the motor i0. The rotor speed at which this effect occurs in revolutions per second equals the frequency of the source I 8 in cycles per second divided by the number of poles of the stator II unless the uni-directional ileld is of sufficient strength to cause the rotor to skip a cycle. In Figure l, as above indicated, this speed is thirty revolutions per second. With a sufficiently strong uni-directional field, the rotor-will skip a cycle. the current induced therein will have a frequency of forty cycles per second and it will run at a speed of twenty revolutions per second or 1200 revolutions per minute.

With a view to providing the uni-directional have eddy currents generated in them which tend` somewhat to act as a drag on the rotor I9. In order to avoid this undesirable drag, the motor construction shown in Figure 2 can be employed. It will be observed that, except for the rotor indicated generally at 33, the motor system shown in Figure 2 is identical with that shown in Figure 1. The rotor 30, instead of employing a relatively Vlarge number of bars, as in the conventional flux component for interacting with the stationary rotor field a direct current component-can be superimposed on the alternating current component in the energizing winding I2. As will hereinafter appear, a separate winding can be employed which is energized entirely by direct current. In either case,'a uni-directional flux component is superimposed on the alternating flux component in the stator II.

The direct current component can be supplied by means of a rectifier, shown generally at 23,

Y which may be of thel copper oxide type. that is connected by conductors 23 and 23 in series circuit relation with the conductor |3. A by-pass resistor 23 is shunted around'the rectifier 23 so as to permit the passage of alternating current through the winding I! as well as direct current through the rectifier 23. As will hereinafter apit will be understood that other types of rectifiersl can be employed. Also. a battery can be em- It will now be apparent that a conventional type oi squirrel cage induction motor I3 can be caused to operate at synchronous speeds of 1800 This can be done either by superimposing a direct current component on the alternating current component in the winding I2 or by providing a separate winding on the stator II for generating therein the unidirectional flux for interacting with the stationary ileld generated by the rotor current in the conductors 20 of the` squirrel cage winding. As a result, the low cost and simplicity of the conventional induction motor construction is retained and, in addition, it is caused to operate at a definite fixed speed without in any way impairsquirrel cage construction, employs only three bars or conductors 3i, 32, and 33 which are conventionally shown as resistors. The bars 3i, 32, and 33 are uniformly spaced about the rotor 33 parallel to its axis and, in effect, form a squirrel cage construction which, because of the provision of the three conductors, furnishes a' three phase rotor construction. At one end the barsA 3l, 32, and 33 are interconnected by a low resistance conductor 33 which may be in the form of a relatively thick disc of copper. The other ends of the bars 3l, 32, and 33 are interconnected by a relatively high resistance connection 33 that may be provided by a relatively thin Idisc of copper. Thus the bars 3I, 32, and 33 .form a star connected squirrel cage rotor construction. The mechanical arrangement of the parts making up the rotor 33, except for the magnetic core, is shown in Figure 2A. ,y

In Figure 3 of the drawings, the motor I3 is essentially the same as shown in Figure 2 except for the means for generating the uni-directional flux in the stator I I. l For this purpose, in Figure 3, an auxiliary winding 33 is provided on the stator II. The winding 33 is inductively related to the winding I2 and preferably is arranged syminetrically therewith. For illustrative purposes, it is shown as being spaced from the winding I2. The auxiliary winding 33. is connected by conductors 33 and'33 through a variable resistor 3| to a rectifier shown generally at 32. The rectifier 32 is of the type previously described, and it serves to permit the now through the auxiliary winding 33 of half cycles of one polarity and prevents flow therethrough ol' .half cycles of opposite polarity. In this manner the auxiliary winding 33 is energized with uni-directional current which generates a uni-directional flux component for operating the rotor 33 ata synchronous speed. The rotor 33 will operate at a speed of 1200 revolutions per minute, or at a'speed of 1800 revolutions per ,i minute, depending upon the strength oi' the unicontrolled by the variable reranged as to introduce the uni-directional flux component independently of the' alternating flux component. As there shown, the motor 33 comprises a stator 33 that is made up of generally rectangular laminations of magnetic material, such as silicon steel. The stator 33 is so constructed that maIn pole members 31 and 33 extend radially inwardly from two sides. and auxiliary pole members 33 and 33 extend radially-inwardly from the other two sides,l all of the pole members conversing on the rotor 33, which has the same ternating current source 51.

construction as previously describedl in connectionwith Figure 2 of the drawings. Shading windings or rings 5l and 52 are. provided on the main pole members 41 and 48 to make the rotor 30 self-starting.

Main windings 53 and 54 are provided on the main pole members 41 and 48, respectively, and are connected in series circuit relation andJ by conductors/55 Aanci 56, are connected across a source 51' of alternating current, such as a 60- cycle l'volt source. It will be understood that the axis of the alternating flux extends between the main pole members 41 and 48 through. the rotor 30.

The auxiliary pole members 49 and 50 are provided for carrying the uni-directional iiux, and it will be observed that its axis is substantially at right angles to lthev axis of the alternating 'iiux. The auxiliary pole members 49 and 50 are energized by auxiliary windings 59 and 60 thereon lwhich are connected in series circuit relation, -and by Aconductors 6i and 62 through a rectifier 63 across the al- A capacitor 64 is connected across the conductors 6| and 62 in order to smooth out the wave form of the direct current applied for energizing the auxiliary windings 59 and 60. Obviously, instead of the rectifier 63 of the copper oxide type illustrated,

other types of rectiflers can be employed. Also, the auxiliary windings 59 and 60 can be energized from a separate current source such as provided by a battery, as will be readily understood.

In Figure 5 of the drawings, another embodiment ci the invention is disclosed. Themotor shown generally at 10 comprises a stator 1I that is formed by a generally rectangular stack of laminations which are so shaped as to provide two pairs of pole members 13-14 and -18 which project inwardly toward a rotor l0 that is similar to the rotor 30 shown in Fig- .ure 2 of the drawings and previously described. Y

Windings 11 and 18 are provided on thel pole members 13 and 14, respectively, and are connected in series circuit relation. Likewise, windings 19 and y80 are provided on pole members 15 and 18, and they are 'connected in series lcircuit relation. 'I'he windings .18 and 80 are commonly connected and they, together with the windings 11 and 19, are connected by conductors 8i, 82, and 83 for energization to a two phase alternatingycurrent source indicated generally at 84. The foregoing construction provides a Apolyphase squirrel cage motor construction in which shading rings, such as shown at 2| and 22 in Figures 2 and 3 of the drawings, are not required for starting purposes.

, In order to provide the uni-directional iiuxv component, a'rectier, shown generally at '85, is

connected by conductors 88 and 81 in conductor 82. 'I'he rectifier 85 is shunted by a variable resistor 88 so as to permit the flow oi' alternating current as well as the direct current from L `the rectifier 85.

` Since certain further changes can be made .shunting said additional winding means through said rectifier means for vcausing uni-directional current to flow therethrough to generate in said stator a uni-directional ux for interacting with kthe iiux generated by current iiow in said rotor winding means to effect rotation of said rotor at a predetermined iixed speed.

2. An alternating current motor comprising, in combination, a, rotor including only three rotor bars uniformly spaced about its periphery and interconnected at one end by relatively high res-istance conducting means and at the other end by relatively low resistance conducting means to provide a star connection, a stator in cooperative relation to said rotor, winding means on said stator, and circuit means for connecting said winding means for energization to an alternating current source.

-3. A synchronous alternating current motor comprising, in combination, a rotor including rotor bars interconnected a`t|one end by relatively high vresistance end ring and at the other end by4 relatively low resistance end ring., a stator in cooperative relation to said rotor, winding means on said stator,- circuit means for connecting said winding means for energization to an alternating current source to generate in said stator and rotor alternating ux components, and means for v erating a uni-directional flux component in said stator for interacting with the alternating ux .compo-nent in said rotor to eil'ect rotation of the same at either 20-or 30 revolutions per second depending upon the' magnitude lof said uni-directional iiux. 'Y

5. A synchronous alternating current motor comprising, in combination, a squirrel cage rotor having only three rotor bars uniformly spaced about its periphery and vconnected together at one in the foregoing described constructions and circuit connections and diiierent embodiments oi the invention can be made without departing from`r the scope thereof, it is intended that an matter shown in the accompanying drawings and described hereinbei'ore shall be interpreted as illustrativeand not in a limiting/sense.

4 I claimas my invention:

1v. A synchronous alternating-current motor comprising, in combination. a stator, winding end with relatively low resistance means providing with said bars a star connection and at .the other end with relatively high resistance means, a two pole stator in cooperative relation to said rotor, winding means on said stator, circuit means for connecting said winding means to a source of single phase alternating current having a frequency of cycles per second whereby said rotor tends to run at a speed approaching 60 revolutions per second, and means for generating a unidirectional iiux component in said stator for interacting withthealternating flux component in said rotor to eiTect rotation of the same at either 20 or @revolutions per second depending source of single phase alternating current having a frequency of 60 cycles per second whereby said rotor tends to run at a speed approaching 60 A revolutions per second, and means for generating a uni-directional flux component in said stator for interacting with the alternating tiux component in said rotor to eii'ect rotation of the same at either 20 or 30 revolutions per second depending upon the magnitude of said uni-direc- 10 tional ux.

EDMUND O. Jl. 

